1. Symantec/
  2. Security Response/
  3. Trojan.Alworo


Risk Level 1: Very Low

June 29, 2011
June 29, 2011 10:08:26 AM
Also Known As:
Troj/Popureb-A [Sophos], Troj/Popureb-B [Sophos], TROJ_POPUREB.SMB [Trend], Troj/PopKmem-A [Sophos]
Infection Length:
84,992 bytes
Systems Affected:
When the Trojan is executed, it modifies the master boot record (MBR) so that it loads the Trojan as well as the original MBR whenever Windows starts.

The Trojan then copies itself to the following location:
%AllUsersProfile%\Documents\My Videos\Van[RANDOM CHARACTERS].tmp

The Trojan creates the following files:
  • %AllUsersProfile%\Documents\My Videos\PulgFile.log
  • %UserProfile%\Application Data\Microsoft\Internet Explorer\Quick Launch\Internet Explorer.IE
  • %UserProfile%\Desktop\Internet Explorer.IE
  • %Windir%\VC.ini

Next, the Trojan creates the following registry entries to alter the home page for certain browsers:
  • HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main\"Default_Page_URL" = "http://123.765321.info"
  • HKEY_CLASSES_ROOT\IE\shell\open\command\"" = "%ProgramFiles%\Internet Explorer\IEXPLORE.EXE http://123.765321.info"
  • HKEY_CLASSES_ROOT\CLSID\{2559a1f4-21d7-11d4-bdaf-00c04f60b9f0}\shell\OpenHomePage\Command\"" = "%ProgramFiles%\Internet Explorer\IEXPLORE.EXE http://123.765321.info"

It also creates the following registry entries:
  • HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run\"Alg" = "C:\Alg.exe"
  • HKEY_CLASSES_ROOT\JE\shell\open\command\"" = "%ProgramFiles%\Internet Explorer\IEXPLORE.EXE "
  • HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Explorer\HideDesktopIcons\ClassicStartMenu\"{871C5380-42A0-1069-A2EA-08002B30309D}" = "2"
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\HideDesktopIcons\NewStartPanel\"{871C5380-42A0-1069-A2EA-08002B30309D}" = "2"
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\HideDesktopIcons\ClassicStartMenu\"{871C5380-42A0-1069-A2EA-08002B30309D}" = "2"
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\HideDesktopIcons\ClassicStartMenu\"{871C5380-42A0-1069-A2EA-08002B30309D}.default" = "1"

The file C:\Alg.exe does not exist in the file system - it is written directly to disk.

The Trojan registers itself as a service with the following characteristics:
Display name: hello_tt
ImagePath: \??\c:\[ORIGINALLY EXECUTED FILE NAME]\hello-tt.sys

It then creates the following registry subkeys for the above service:
  • HKEY_LOCAL_MACHINE\system\CurrentControlSet\Services\hello_tt
  • HKEY_LOCAL_MACHINE\system\CurrentControlSet\Enum\Root\LEGACY_HELLO_TT

Note: The file hello-tt.sys does not exist in the file system - it is written directly to disk.

Next, the Trojan deletes the following registry entries:
  • HKEY_CLASSES_ROOT\CLSID\{2559a1f4-21d7-11d4-bdaf-00c04f60b9f0}\Instance\InitPropertyBag\"InitString"
  • HKEY_CLASSES_ROOT\CLSID\{1f4de370-d627-11d1-ba4f-00a0c91eedba}\ShellFolder\"Attribute"
  • HKEY_CLASSES_ROOT\CLSID\{1f4de370-d627-11d1-ba4f-00a0c91eedba}\InProcServer32\""
  • HKEY_CLASSES_ROOT\CLSID\{1f4de370-d627-11d1-ba4f-00a0c91eedba}\InProcServer32\"ThreadingModel"
  • HKEY_CLASSES_ROOT\CLSID\{1f4de370-d627-11d1-ba4f-00a0c91eedba}\DefaultIcon\""
  • HKEY_CLASSES_ROOT\CLSID\{1f4de370-d627-11d1-ba4f-00a0c91eedba}\""
  • HKEY_CLASSES_ROOT\CLSID\{1f4de370-d627-11d1-ba4f-00a0c91eedba}\"LocalizedString"
  • HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Explorer\NameSpace\{1f4de370-d627-11d1-ba4f-00a0c91eedba}\""

The Trojan modifies the following registry entries to alter the home page for certain browsers:
  • HKEY_CLASSES_ROOT\CLSID\{871C5380-42A0-1069-A2EA-08002B30309D}\shell\OpenHomePageCommand\"" = "%ProgramFiles%\Internet Explorer\IEXPLORE.EXE http://123.765321.info"
  • HKEY_CLASSES_ROOT\CLSID\{2559a1f4-21d7-11d4-bdaf-00c04f60b9f0}\DefaultIcon\"" = "%ProgramFiles%\Internet Explorer\IEXPLORE.EXE"
  • HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main\"Start Page" = "http://123.765321.info"

It also modifies the following registry entries:
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced\"HideFileExt" = "1"
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced\"Hidden" = "2"
  • HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Explorer\HideDesktopIcons\NewStartPanel\"{871C5380-42A0-1069-A2EA-08002B30309D}" = "2"
  • HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Explorer\HideDesktopIcons\ClassicStartMenu\"{871C5380-42A0-1069-A2EA-08002B30309D}.default" = "1"

The Trojan then monitors the following processes and may change the URL to http://123.765321.info:
  • 115br.exe
  • 13511.exe
  • 360se.exe
  • chrome.exe
  • firefox.exe
  • iexplore.exe
  • maxthon.exe
  • sogouexplorer.exe
  • theworld.exe
  • ttraveler.exe

It may then display advertisements in the running browsers.

The Trojan is able to silently open an Internet Explorer process to connect to a specified URL.

Next, the Trojan downloads configuration files from the following locations on TCP port 83:
  • http://1.dh818.info
  • http://2.dh818.info

It attempts to change the home page of the following browsers to http://123.765321.info:
  • Chrome
  • FireFox
  • Internet Explorer
  • Maxthon
  • Sogou Explorer

Next, the Trojan attempts to connect to the following locations to download configuration and advertisement information:
  • [http://]1.dh818.info:83/2/logo[REMOVED]
  • [http://]1.dh818.info:83/2/pop[REMOVED]

The Trojan then sends the MAC address and OS version of the compromised computer to the following location:
http://2.dh818.info:83/sms/do.php?userid=[MAC ADDRESS]&time=[CURRENT DATE AND TIME]&msg=[RANDOM CHARACTERS]&ver=&os=[OPERATING SYSTEM VERSION]&fy=1&pauid=[RANDOM NUMBER]&checkId=[RANDOM NUMBER]


Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
  • Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media.
  • Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.
Writeup By: Masaki Suenaga, Karthik Servaraj, Piotr Krysiuk, Stephen Doherty
Summary| Technical Details| Removal

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